Acrylic graft copolymers and coating compositions thereof

ABSTRACT

A graft copolymer having a polymeric backbone with pendent hydroxyl groups; wherein the hydrogen atom of at least the one the hydroxyl groups is replaced by the formula ##STR1## where R is an aliphatic group, a cycloaliphatic group or an aromatic group; R 1  is an alkylene group having 2-6 carbon atoms; R 2  is a polymer segment of a vinyl addition polymer, such as butyl acrylate/hydroxyethyl acrylate; coating compositions of this copolymer can be cross-linked with conventional cross-linking agents such as an alkylated melamine formaldehyde resin or an organic polyisocyanate and coating compositions useful for flexible elastomeric substrates can be prepared from this copolymer.

BACKGROUND OF THE INVENTION

This invention is related to graft copolymers, a process for makingthese copolymers and to coating compositions containing thesecopolymers.

Certain uses for polymers require that the polymer have severalparticular characteristics; for example, finishes for flexibleelastomeric trim parts for modern automobiles and trucks require a filmforming polymer with characteristics that provide a flexible finishafter the finish is fully cured and that provide a finish that hasexcellent adhesion, durability and weatherability. Conventionalpolymerization techniques have been found to be inadequate to formpolymers having characteristics such as are required for flexiblefinishes. The process of this invention forms novel polymers havingthese characteristics for flexible finishes and for other finishes andcan be used to form polymers for other uses.

SUMMARY OF THE INVENTION

A graft copolymer having a polymeric backbone with pendent hydroxylgroups, wherein the hydrogen atom of at least one of the hydroxyl groupsis replaced by the following formula: ##STR2## where R is an aliphaticgroup, a cycloaliphatic group or an aromatic group; R¹ is an alkylenegroup having 2-6 carbon atoms, R², which forms a side chain of the graftcopolymer, is a polymer segment of a vinyl addition polymer.

Coating compositions of this copolymer and a process for making thiscopolymer are also part of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The graft copolymer has a polymeric backbone and at least one polymericside chain pending from the backbone. A mercapto organic isocyanate isused to link the backbone with the side chain. By varying thecomposition of the backbone and side chain(s), graft copolymers can bedesigned for a wide variety of uses. In particular, the graft copolymercan be used as a film forming constituent in coating compositions. Forexample, flexible coating compositions which have excellent adherence tononmetallic substrates and are flexible and durable now can be madeusing the graft copolymers as the film forming constituent or as one ofthe film forming constituents.

By using selected monomers in the backbone and side chain(s) of thegraft copolymer, solution coating compositions, aqueous coatingcompositions or organosol coating compositions can be formed. Forsolution coating composition, a graft copolymer is used in which boththe backbone and side chain(s) are soluble in the solvent used for thecoating composition. In an organosol coating composition, either thebackbone or preferably the side chain(s) of the graft copolymer issoluble in the solvent used in the coating composition. In an aqueouscoating composition, hydroxy and carboxyl groups from either thebackbone or side chain(s) or both can be used to solubilize or dispersethe copolymer. Generally, in an aqueous coating composition, ammonia oran amine is used to form a salt of the copolymer which readily dispersesin water.

In one method for preparing the graft copolymer, a mercapto organicisocyanate is reacted at about 80°-150° C. for about 0.5-6 hours, withusually a conventional catalyst, with ethylenically unsaturated monomerswhich polymerize by vinyl addition reaction to form an isocyanateterminated polymer. A polymer containing pendent hydroxy groups isprepared and the isocyanate terminated polymer is reacted with pendenthydroxyl groups of hydroxyl containing polymer to form the graftcopolymer. The polymer containing pendent hydroxyl groups forms thebackbone of the graft copolymer and the isocyanate terminated polymerforms the side chain(s) of the graft copolymer.

In the preferred method for preparing the graft copolymer, the mercaptoorganic isocyanate is added to a hydroxyl containing polymer usually inthe presence of a catalyst to form a polymer with reactive mercaptogroups. The reaction is carried out at about 80°-150° C. for about 0.5-6hours. Typical catalysts that can be used are stannous acetate, butyltin oxide or dibutyl tin dilaurate. This polymer containing reactivemercapto groups is reacted with ethylenically unsaturated monomers whichpolymerize by vinyl addition polymerization to form the graft copolymer.The reaction is carried out at about 60°-150° C. for about 1-6 hours andusually a catalyst is used. Typical catalysts are used at about 0.1-4%by weight of the polymerizable constituents used to prepare the graftcopolymer and are for example, azobisisobutyronitrile azobisdimethylvaleronitrile, benzoyl peroxide, tertiary butyl peroxy pervalate. Up to5 percent by weight of a chain transfer agent such as dodecyl mercaptonor benzene thiol can be used to control the molecular weight of thegraft copolymer.

The graft copolymer has a weight average molecular weight of about 5,000to 1,000,000 determined by gel permeation chromatography. The graftcopolymer contains about 25-95% by weight of backbone and about 5-75% byweight of side chain(s). Preferably, the graft copolymer contains about50-90% by weight of backbone and about 10-50% by weight of sidechain(s).

The mercapto organic isocyanate is prepared by reacting one mole ofmercapto alkanol with one mole of an organic diisocyanate at about50°-120° C. for about 20 to 240 minutes. Usually a solvent such astoluene, xylene, ethyl acetate, butyl acetate or the like is used. Also,a catalyst such as p. toluene sulfonic acid, butyl acid phosphate,acetic acid is used. To determine when the mercapto organic isocyanatehas been formed, an infrared spectrophotometer can be used to measurethe amount of unreacted hydroxyl and isocyanate group in a sample.Generally, when the absorbence ratio of carbonyl to isocyanate reachesabout 0.5, the reaction is complete and the mercapto organic isocyanatehas been formed. The resulting mercapto organic isocyanate has theformula ##STR3## where R is an aliphatic, cycloaliphatic or aromaticgroup and R¹ is an alkylene group having 2-6 carbon atoms.

Typical mercapto alkanols that can be used have 2-6 carbon atoms and areas follows: 1,2-mercaptoethanol, 1,2 and 1,3 mercaptopropanol,mercaptoisopropanol, 1,4-mercaptobutanol, mercaptoisobutanol, 1,5mercaptopentanol, 1,6-mercaptohexanol and the like.

Typical organic diisocyanates that can be used are as follows:isophorone diisocyanate which is3-isocyanate-methyl-3,5,5-trimethyl-cyclohexyl-isocyanate,

propylene-1,2-diisocyanate,

butylene-1,2-diisocyanate,

butylene-1,3-diisocyanate,

methyl-2,6-diisocyanato caproate,

hexamethylene diisocyanate,

2,4,4-trimethylhexamethylene diisocyanate

octamethylene diisocyanate,

2,2,4-trimethylhexamethylene diisocyanate

nonamethylene diisocyanate,

decamethylene diisocyanate,

2,11-diisocyano-dodecane and the like,

meta-phenylene diisocyanate,

para-phenylene diisocyanate,

toluene-2,4-diisocyanate,

toluene-2,6-diisocyanate,

xylene-2,4-diisocyanate,

xylene-2,6-diisocyanate,

dialkyl benzene diisocyanates, such as methylpropylbenzene diisocyanate,methylethylbenzene diisocyanate, and the like;

2,2'-biphenylene diisocyanate,

3,3'-biphenylene diisocyanate,

4,4'-biphenylene diisocyanate,

3,3'-dimethyl-4,4'-biphenylene diisocyanate, and the like;

methylene-bis-(4-phenyl isocyanate),

ethylene-bis-(4-phenyl isocyanate),

isopropylidene-bis-(4-phenyl isocyanate),

butylene-bis-(4-phenylisocyanate),

hexafluoroisopropylidene-bis-(4-phenyl isocyanate), and the like;

2,2'-oxydiphenyl diisocyanate,

3,3'-oxydiphenyl diisocyanate,

4,4'-oxydiphenyl diisocyanate,

2,2'-ketodiphenyl diisocyanate,

3,3'-ketodiphenyl diisocyanate,

4,4'-ketodiphenyl diisocyanate,

2,2'-thiodiphenyl diisocyanate,

3,3'-thiodiphenyl diisocyanate,

4,4'-thiodiphenyl diisocyanate, and the like;

2,2'-sulfonediphenyl diisocyanate,

3,3'-sulfonediphenyl diisocyanate,

4,4'-sulfonediphenyl diisocyanate, and the like

2,2'-methylene-bis-(cyclohexyl isocyanate),

3,3'-methylene-bis-(cyclohexyl isocyanate),

4,4'-methylene-bis-(cyclohexyl isocyanate),

4,4'-ethylene-bis-(cyclohexyl isocyanate),

4,4'-propylene-bis-(cyclohexyl isocyanate),

bis-(para-isocyano-cyclohexyl)sulfide,

bis-(para-isocyano-cyclohexyl)sulfone,

bis-(para-isocyano-cyclohexyl)ether,

bis-(para-isocyano-cyclohexyl)diethyl silane,

bis-(para-isocyano-cyclohexyl)diphenyl silane,

bis-(para-isocyano-cyclohexyl) ethyl phosphine oxide

bis-(para-isocyano-cyclohexyl)phenyl phosphine oxide

bis-(para-isocyano-cyclohexyl)N-phenyl amine,

bis-(para-isocyano-cyclohexyl)N-methyl amine,

bis-(4-isocyano-phenyl)diethyl silane,

bis-(4-isocyano-phenyl)diphenyl silane,

dichloro-biphenylene diisocyanate,

bis-(4-isocyano-phenyl)ethyl phosphine oxide,

bis-(4-isocyano-phenyl)phenyl phosphine oxide

bis-(4-isocyano-phenyl)-N-phenyl amine,

bis-(4-isocyano-phenyl)-N-methyl amine,

3,3'-dimethyl-4,4'-diisocyano biphenyl,

3,3'-dimethoxy-biphenylene diisocyanate,

2,4-bis-(β-isocyano-t-butyl)toluene,

bis-(para-β-isocyano-t-butyl-phenyl)ether,

para-bis-(2-methyl-4-isocyano-phenyl)benzene,

para-bis-(1,1-dimethyl-5-amino-pentyl)benzene,

3,3'-diisocyano adamantane,

3,3'-diisocyano biadamantane,

3,3'-diisocyanoethyl-1,1'-biadamantane,

1,2-bis-(3-isocyano-propoxy)ethane,

2,2-dimethyl propylene diisocyanate,

3-methoxy-hexamethylene diisocyanate

2,5-dimethyl heptamethylene diisocyanate,

5-methyl-nonamethylene diisocyanate,

1,4-diisocyano-cyclohexane,

1,2-diisocyano-octadecane,

2,5-diisocyano-1,3,4-oxadiazole,

Ocn(ch₂)₃ o(ch₂)₂ o(ch₂)₃ nco,

ocn(ch₂)₃ s(ch₂)₃ nco and ##STR4##

Isophorone diisocyanate is preferred since it reacts rapidly and forms astable intermediate.

Polymers used for the backbone of the graft copolymer contain functionalhydroxyl groups. These polymers can be acrylic polymers, polyesters,styrene/allyl alcohol copolymers, phenoxy resins, epoxy resins such ascondensates of epichlorohydrin and bisphenol A, epoxyester polymers,cellulosic polymers such as cellulose acetate butyrate, celluloseacetate propionate, nitro cellulose, partially hydrolyzed polyvinylacetate, oil free alkyd resins, drying oil alkyd resins,ethylenepropylene oxide polymers and polyalkylene ether glycol.

The polymeric side chains of the graft copolymer can be any of a widevariety of monomers that polymerize by a vinyl addition reaction.Typically useful monomers are as follows: ethylene, propylene, butylene,vinyl chloride, vinylidene chloride, tetrafluoroethylene,trifluorochoroethylene, tetrafluoroethylene/hexafluoropropylene,tetrafluoroethylene/perfluorovinylether, vinyl acetate, styrene, allylalcohol, styrene/allyl alcohol, alkyl acrylates or methacrylates having1-18 carbon atoms in the alkyl group, hydroxy alkyl acrylates ormethacrylates having 1-12 carbon atoms in the alkyl group, acrylamide,methacrylamide, acrylonitrile, methacrylonitrile, methacrylic acid,acrylic acid, itaconic acid and mixture of the above monomers.

One typically useful graft copolymer prepared according to the processof this invention comprises a graft copolymer in which the backbone isof an alkyl acrylate or methacrylate and a hydroxy alkyl acrylate ormethacrylate and in which the side chains are of an alkyl acrylate ormethacrylate and a hydroxy alkyl acrylate or methacrylate.

Alkyl acrylates and methacrylates that can be used to prepare this graftcopolymer are methyl methacrylate, ethyl methacrylate, propylmethacrylate, isopropyl methacrylate, butyl methacrylate, isobutylmethacrylate, tertiary buty methacrylate, hexyl methacrylate,2-ethylhexy methacrylate, lauryl methacrylate, ethyl acrylate, propylacrylate, butyl acrylate, hexyl acrylate, octyl acrylate and the like.Typically useful hydroxy alkyl acrylate and methacrylates arehydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutylmethacrylate and the like. Ethylenically unsaturated carboxylic acidssuch as acrylic acid and methacrylic acid can also be used.

Typically examples of polymers of this type are as follows:

(1) a graft copolymer having a backbone of methyl methacrylate/2 hydroxyethyl methacrylate and side chains of butyl acrylate 2-hydroxyethylacrylate;

(2) a graft copolymer having a backbone of butyl acrylate/hydroxyethylacrylate and side chains of methyl methacrylate/butylacrylate/hydroxyethyl acrylate/acrylic acid.

Another useful graft copolymer has a backbone of styrene/allyl alcoholand side chains of an alkyl acrylate or methacrylate. One typical graftcopolymer of this type has a backbone of styrene/allyl alcohol and sidechains of 2 ethylhexyl acrylate.

One useful water dispersible graft copolymer has a backbone of astyrene/allyl alcohol ester and side chains of an ethylenicallyunsaturated carboxylic acid. A typical graft copolymer of this type hasa backbone of styrene/allyl alcohol esterified with a drying oil fattyacid such as linoleic acid and side chains of polymerized methacrylicacid or acrylic acid.

Another useful graft copolymer has a polyester backbone and side chainsof polymerized acrylic monomers. The polyester is of a polyol or amixture of polyols and a dicarboxylic acid and the side chains can be ofany of the aforementioned acrylic monomers.

One useful graft copolymer of this type has a backbone of polyester ofneopentyl glycol/trimethylol propane/azelaic acid and side chains ofmethyl methacrylate/butylacrylate/hydroxyethyl acrylate/acrylic acid.

In another useful graft copolymer, the backbone is a cellulosic polymerhaving reactive hydroxyl groups and the side chains are any of theaforementioned alkyl acrylates or methacrylates, hydroxy alkyl acrylatesor methacrylates or mixtures thereof. One useful graft copolymer of thistype has a backbone of cellulose acetate butyrate and side chains ofmethyl methacrylate/butyl acrylate.

When the graft copolymer is used in coating compositions for flexiblesubstrates, described hereinafter, the graft copolymer should have anelongation at break of at least 15%, preferably, 15-50%.

Conventional solvents can be used to prepare the graft copolymer and todilute the graft copolymer, or coating compositions prepared from thegraft copolymer and are as follows: toluene, xylene, butyl acetate,ethyl acetate, acetone, methyl ethyl ketone, methylisobutyl ketone, andother aromatic hydrocarbons, cycloaliphatic hydrocarbons, esters,ethers, and ketones such as are conventionally used.

Coating compositions prepared with the graft copolymer contain as thefilm forming constituents about 50-95% by weight of the graft copolymerand about 5-50% by weight of a cross-linking agent. Generally thesecoating compositions have a solids content of film forming constituentof about 5-60% by weight.

The cross-linking agent used in the coating composition is compatiblewith the graft copolymer and can either be an alkylated melamineformaldehyde resin or a polyisocyanate. Typical alkylated melamineformaldehyde resins have one to eight carbon atoms in the alkyl groupand are resins that are well known in the art. These resins are preparedby conventional techniques in which a lower alkyl alcohol such asmethanol, ethanol, butanol, isobutanol, propanol, isopropanol, hexanol,2-ethyl hexanol and the like is reacted with a melamine formaldehyde toprovide pendent alkoxy groups.

Preferred melamine resins that are used are butylated melamineformaldehyde resins, methylated/butylated melamine formaldehyde resinsand hexa(methoxymethyl) melamine resin.

An acid catalyst can be used in the coating composition such aspara-toluene sulfonic acid or butyl acid phosphate. An acid catalyst isneeded if there is an absence of acid groups in the graft copolymer ofif a low temperature cure is required or if a highly etherified melamineresin is used such as hexa(methoxymethyl)melamine.

A variety of organic polyisocyanates can be used as the crosslinkingagent in the coating composition and include the aforementionedisocyanates and other aliphatic, cycloaliphatic, heterocyclicpolyisocyanates. Typical polyisocyanates are, for example,methylene-bis-(4-cyclohexylisocyanate), tetramethylene diisocyanate,hexamethylene diisocyanate, ethylene diisocyanate,cyclohexylene-1,2-diisocyanate, and the like.

Polyisocyanates of a biuret, for example, the biuret of hexamethylenediisocyanate made according to Mayer et al. U.S. Pat. No. 3,245,941,issued Apr. 12, 1966 can also be used.

Organic plasticizers can also be used in the coating composition inamounts up to 1-10 percent by weight based on the weight of film-formingconstituents. Monomeric and polymeric plasticizers can be used such asphthalate ester plasticizers, and in particular, alkyl and cycloalkylester phthalates in which the alkyl groups have 2-10 carbon atoms suchas dioctyl phthalate, didecyl phthalate, butyl benzylphthalate,dicyclohexyl phthalate and mixtures thereof. Epoxidized soya bean oil,oil free and oil modified alkyds can also be used as plasticizers.Polyester resins such as alkylene glycol esters of adipic and benzoicacid, for example, ethylene glycol adipate benzoate, ethylene glycoladipate benzoate phthalate, can also be used in the coating compositionof this invention.

The coating composition can be pigmented. Typical pigments which can beused are metallic oxides, preferably titanium dioxide, zinc oxide, ironoxide, and the like, metallic flakes, such as aluminum flake, metallicpowders, metallic hydroxides, "Afflair" pigments, i.e., mica coated withtitanium dioxide, sulfates, carbonates, carbon blacks, silica, talc,china clay and other pigments, organic dyes and lakes.

Other compatible resins can be incorporated into the coating compositionsuch as vinyl chloride copolymers, polyurethanes, cellulose acetatebutyrate, and silicone resins. Also, ultraviolet light stabilizers canbe incorporated into the coating composition.

If the coating composition is formed into a water based finish by usingacid constituents in the graft copolymer, the acid constituents areneutralized with ammonia or an amine such as diethylethanol amine andwater is added to form the composition. Any of the aforementionedadditives, resins, plasticizers and pigments can be incorporated intothe aqueous composition by using conventional techniques.

A primer composition is usually applied to the substrate before theabove coating composition is applied. Any of the conventional alkydresin, epoxy resin or epoxy ester resin primers can be used. Inparticular when the coating composition is used over a flexiblesubstrate, a primer of a hydroxyl terminated polyalkylene ether glycolcross-linked with an aromatic diisocyanate or a polyester chain-extendedwith an organic diisocyanate and cross-linked with an alkylated melamineformaldehyde resin is used.

Preferred primers for flexible substrates are as follows: a hydroxylterminated polypropylene ether glycol cross-linked with toluenediisocyanate and an isophthalate polyester chain-extended withmethylene-bis-(cycloxyl isocyanate) cross-linked with alkylate melamineformaldehyde resin.

Any of the aforementioned pigments and other additives can be added tothe primers. Preferably, carbon black and extender pigments are used inthe primer.

The flexible substrate may be any one of the well-known polyvinylchloride, polyurethanes or unsaturated or saturated hydrocarbonelastomers, e.g., ethylenepropylene copolymer elastomers, particularlyone that is made sulfur curable by the inclusion of 1-10 percent byweight nonconjugated diene, because of their better resistance tooxidative and thermal aging. Butyl rubber, styrene-butadiene rubber,polybutadiene rubber or polyisoprene rubber (either natural orsynthetic) are also used. Typical ethylene-propylene rubbers are thosecopolymers containing 50-75 weight percent ethylene, 25-45 weightpercent propylene, and 2-8 weight percent non conjugated diene such as1,4-hexadiene, 5-ethylidene-2-norbornene or dicylopentadiene.

To prepare a coated article with the coating composition, a primer, ifused, is applied by conventional techniques to the substrate by theusual application methods such as spraying, electrostatic spraying,dipping, brushing, flow-coating and the like. The primer is then bakedat 95° to 145° C. for 5 to 60 minutes. The coating composition is thenapplied by one of the aforementioned application methods and baked at95° to 130° C. for 15 to 60 minutes.

The following Examples illustrate the invention. All quantities are on aweight basis unless otherwise indicated.

EXAMPLE 1

The following constituents are changed into a reaction vessel equippedwith a reflux condenser, thermometer and stirrer:

    ______________________________________                                        Portion 1                                                                     Toluene                   100.00g                                             p Toluene sulfonic acid   0.01g                                               2-Mercaptoethanol         2.35g                                               Portion 2                                                                     Isophorone diisocyanate   6.70g                                               Total                     109.06g                                             ______________________________________                                    

Portion 1 is changed into the reaction vessel and dried azeotropicallyby heating Portion 1 to its reflux temperature for 75 minutes. Portion 2is added and the resulting reaction mixture is held at about 100° C. Asample is removed after about 1.5 hours and analyzed on an infraredspectophotometer to determine the carbonyl to isocyanate absorbanceratio. The reaction mixture is held at 100° C. until the carbonyl toisocyanate absorbance ratio of a sample reaches about 0.50.

The resulting mercapto isocyanate solution has a 8.25% by weight solidscontent.

GRAFT COPOLYMER SYNTHESIS

The following constituents are changed into a reaction vessel equippedwith a reflux condenser, a stirrer and thermometer:

    ______________________________________                                        Portion 1                                                                     Copolymer solution (47% solids)                                                                         188.00g                                             ______________________________________                                    

of a methyl methacrylate/2-hydroxy ethyl methacrylate copolymer 85/15ratio, having an inherent viscosity of 0.429 measured at 0.5% solids indichloroethylene, and the solvent is a 70/30 mixture of toluene/ethylacetate)

    ______________________________________                                        Stannous octoate          0.01cc                                              Mercapto isocyanate solution                                                                            7.76g                                               (prepared above)                                                              Portion 2                                                                     Butyl acrylate            90.00g                                              2-Hydroxyethylacrylate    10.00g                                              Portion 3                                                                     Azobisisobutyronitrile    0.35g                                               Toluene                   25.00g                                              ______________________________________                                    

Portion 1 is charged into the reaction vessel and heated for about 6hours. No isocyanate groups are observed in a sample analyzed by aninfrared spectrophotometer. Portion 2 is charged into the reactionvessel and then Portion 3 is charged into the vessel at the rate of 5 gevery 30 minutes until Portion 3 is depleted while holding the resultingreaction mixture at its reflux temperature. After the addition ofPortion 3, the reaction mixture is held at its reflux temperature for anadditional 30 minutes.

The resulting composition has a polymer solids content of about 53% andthe polymer is of 66 parts of methyl methacrylate/2-hydroxyethylacrylate (90/10 ratio) and 33 parts of butylacrylate/2-hydroxyethyl acrylate (90/10 ratio) and has an inherentviscosity measured as above of 0.78 and a weight average molecularweight determined by gel permeation chromatography of about 200,000.

About 37.6 parts of the polymer solution is blended with about 37.6parts of the polymer solution is blended with about 6.4 parts of a 75%by weight the biruet of hexamethylene diisocyanate in acetone solvent toform a coating composition. This coating composition is sprayed onto aprimed metal substrate and baked at 120° C. for 30 minutes. Theresulting finish has a hardness of 7.8 knoops.

A film of the coating composition is drawn down on a glass plate, bakedas above and removed and the following physical properties are measuredon an Instron Tensil Testing Machine:

    ______________________________________                                        % Elongation at break  15                                                     (measued at 25° C.)                                                    Tensile Strength       4500 pounds                                                                   per square                                                                    inch (psi)                                             Initial Modulus        130,000 psi.                                           ______________________________________                                    

EXAMPLE 2

The following constituents are changed into a reaction vessel equippedas in Example 1 to form a mercapto terminated copolymer solution:

    ______________________________________                                        Copolymer solution        185g                                                ______________________________________                                    

(54.0% solids of a butyl acrylate/hydroxy hydroxyethyl acrylate(BA/HEA), weight ratio 93/7 having a inherent viscosity of 0.25 measuredas in Example 1, in toluene)

    ______________________________________                                        Dibutyl tin dilaurate     0.10g                                               Mercapto isocyanate solution                                                                            109.00g                                             (prepared in Example 1)                                                       ______________________________________                                    

The above mixture is heated for 6 hours at 110° C. A sample of themixture is removed and analyzed on an infrared spectophotometer. Noisocyanate absorption was observed on the infrared spectra whichindicates that the isocyanate groups have reacted with the hydroxylgroups of the copolymer.

A monomer mixture is prepared by blending the following monomers:

    ______________________________________                                        methyl methacrylate (MMA)  52g.                                               butyl acrylate (BA)        29g.                                               hydroxyethyl acrylate (HEA)                                                                              13g.                                               acrylic acid (AA)          6g.                                                ______________________________________                                    

Sixty grams of the above monomer mixture are added to the above preparedmercapto terminated copolymer solution and the resulting reactionmixture is heated to its reflux temperature. The remainder of monomermixture is blended with 0.40 grams of azobisisobutyronitrile and 20grams of toluene and this mixture is slowly added to the above reactionmixture over a 3 hour period while maintaining the reaction mixture atits reflux temperature. About 1 hour, 2 hours and 2.5 hours after thereaction mixture is heated to its reflux temperature, 50 gram portionsof n-butanol are added to reduce the viscosity of the solution. At theend of the reaction, a final portion of 150 g of butanol is added tocool the reaction mixture. The resulting graft copolymer solution has asolids content of 27.6%. The resulting graft copolymer has a inherentviscosity of 0.73 measured as in Example 1. The graft copolymer solutionis clear and provides a clear film 2 mil thick film on glass when bakedat 120° C. for 30 minutes.

The graft copolymer has a calculated compositive of 33.1% BA/HEA(93/7),5.5% mercaptoisocyanate 61.4% MMA/BA/HEA/AA(52/29/13/6) and has a weightaverage molecular weight of about 200,000 determined by gel permeationchromatography.

Butylated melamine formaldehyde solution is blended with the above graftcopolymer solution to provide a coating composition in which the ratioof graft copolymer to butylate melamine formaldehyde is 87/13. Thecoating composition is sprayed onto a primed metal substrate and bakedat 120° C. for 40 minutes. The resulting finish has a hardness of about2.1 knoops.

A film of the above coating composition is cast on a glass substrate andbaked as above and removed and its physical properties are measured onan Instron Tensile Testing Machine at different temperatures. Theresults are as follows:

    ______________________________________                                                                         Initial                                      Test      % Elongation                                                                             Tensile     Modulus                                      Temperature                                                                             at Break   Strength (psi)                                                                            (psi)                                        ______________________________________                                        65° C.                                                                           17         281         2200                                         23° C.                                                                           36         1100        6200                                         -18° C.                                                                          15         1800        21,000                                       -28° C.                                                                          8          2200        55,000                                       ______________________________________                                    

EXAMPLE 3

A graft copolymer having a styrene/allyl alcohol backbone and poly2-ethylhexylacrylate can be prepared by changing the followingconstituents into a polymerization vessel equipped as in Example 1:

    ______________________________________                                        Styrene/allyl alcohol copolymer                                                                           80g                                               solution (50% solids in which the copolymer                                   has a number average molecular weight of                                      1600, a weight average molecular weight                                       2340, both determined by gel permeation                                       chromotography, 5.7% hydroxyl content                                         and a ratio of 5.3 moles of allyl alcohol                                     to 12.3 moles of styrene)                                                     Mercapto isocyanate solution                                                                              100g                                              (prepared in Example 1)                                                       Dibutyltin dilaurate        0.1g                                              ______________________________________                                    

The above mixture should be heated for about 3 hours at about 110° C.and a mercapto functional styrene/allyl alcohol copolymer should result.

To the above prepared mercapto functional styrene/allyl alcoholcopolymer solution, a mixture of about 0.1 g of azobisisobutyronitrileand 20 g of 2 ethylhexyl acrylate should be added at a uniform rate overa 3 hour period while maintaining the resulting reaction mixture atabout 95°-100° C. The reaction should be continued for an additional 30minutes to form a graft copolymer having a backbone of styrene/allylalcohol and side chains of poly 2-ethylhexyl acrylate.

The resulting graft copolymer solution can be converted into a stableorganosol by the addition of heptane. Butylated melamine resin can beadded to both the organosol of the graft copolymer or solution of thegraft copolymer to form a coating composition that can be baked atmoderate temperatures to a hard glossy chemically resistant finish.

EXAMPLE 4

A water dispersible styrene/allyl alcohol ester graft copolymer havingmethacrylic acid side chains can be prepared by charging the followingconstitutents into a reaction vessel equipped as in Example 1.

    ______________________________________                                        Portion 1                                                                     ______________________________________                                        Styrene allyl alcohol copolymer                                                                          100g                                               solution (described in Example 3)                                             Linoleic Acid              56g                                                Xylene                     50g                                                ______________________________________                                    

    ______________________________________                                        Portion 2                                                                     ______________________________________                                        Mercapto isocyanate        60g                                                solution (prepared in Example 1)                                              Dibutyltin dilaurate       0.01g                                              ______________________________________                                    

Portion 1 should be heated to its reflux temperature and reacted untilthe acid number of the mixture is about 5 milligrams KOH per gram ofsample. Portion 2 should then be added and the reaction mixture shouldbe heated to about 110° C. and held at this temperature for about 3hours.

A graft copolymer can be prepared by adding methacrylic acid monomer tothe above prepared reaction mixture along with a catalyst ofazobisisobutyronitrile and then reacting the constituents at about 90°C. for about 2 hours to provide a graft copolymer with an acid number ofabout 30.

The resulting graft copolymer should be neutralized with dimethylethanolamine and then water can be added to form a dispersion. The resultingdispersion should be stable even when stored for an extended period at60° C.

A useful coating composition can be prepared from this dispersion by theaddition of a sufficient amount of a conventional cobalt dryer. Filmsfrom this coating composition should dry in about 24 hours to a hard,glossy, durable and weatherable finish.

EXAMPLE 5

A polyester graft copolymer having acrylic side chains can be preparedby charging the following constituents into a reaction vessel equippedas in Example 1.

    ______________________________________                                        Neopentyl glycol          1248g                                               Trimethylol propane       295g                                                Azelaic acid              2331g                                               ______________________________________                                    

The above mixture of constituents should be heated to and held at about230° C. while removing water from the mixture until a polyester isformed having an acid number of about 7.

About 50 grams of the mercaptoisocyanate solution prepared in Example 1along with 0.01 g of dibutyltin dilaurate should be added to about 40grams of the above prepared polyester and heated for about 3 hours at100° C. to form a polyester having reactive mercapto groups.

A graft copolymer then can be prepared by adding the above polyesterwith reactive mercapto groups to the following mixture of acrylicmonomers and catalysts over a 3 hour period while holding the resultingreaction mixture at about 100°-105° C. The mixture of acrylic monomersand catalyst is as follows:

    ______________________________________                                        Methyl methacrylate        30g                                                Butyl acrylate             15g                                                Hydroxyethyl acrylate      15g                                                Acrylic Acid               1g                                                 Azobisisobutyronitrile     0.3g                                               ______________________________________                                    

The resulting polyester graft copolymer having acrylic side chains canbe formed into a coating composition with a methylated melaminecrosslinking resin which can be applied and baked as in Example 1 toform a durable flexible finish. These finishes can be used over flexiblehydrocarbon rubber or polyvinyl chloride substrates with appropriateprimers to provide finishes of excellent flexibility and toughness.

EXAMPLE 6

A cellulose acetate butyrate graft copolymer having acrylic side chainscan be prepared by using the reaction vessel equipped as in Example 1. Asolution of 40 g of cellulose acetate butyrate having a 2% acetylcontent, a 53% butyryl content, a 1.6% hydroxyl content and a 0.2 secondviscosity measured according to ASTMD-817-65 is charged into thereaction vessel. A sufficient amount of the mercapto isocyanate solutionprepared in Example 1 should be added to react with the hydroxyl groupsof the cellulose acetate butyrate along with about 0.01 g of dibutyltindilaurate. The above constituent should be reacted for about 3 hours atabout 110° C. to form a cellulose acetate butyrate polymer havingreactive mercapto groups.

A graft copolymer then can be prepared by adding the following mixtureto the above cellulose acetate butyrate polymer having reactive mercaptogroups over a 3 hour period while holding the reaction temperature atabout 100°-105° C.

    ______________________________________                                        Methyl methacrylate monomer                                                                              40g                                                Butyl acrylate monomer     20g                                                Azobisisobutyronitrile     0.3g                                               ______________________________________                                    

The reaction should be continued for an additional 30 minutes after theabove monomer mixture is added. The resulting graft copolymer shouldhave acrylic side chains and a cellulose acetate butyrate backbone.

The resulting graft copolymer can be used in coating compositions withor without conventional cross-linking agents. A lacquer of the graftcopolymer can be prepared which forms a high quality tough andtransparent finish for wood.

[Note: Examples 3-6 were not conducted in a laboratory but one skilledin the art should obtain the compositions as set forth therein.

I claim:
 1. A graft copolymer consisting essentially of about 25-95% byweight of an acrylate polymer backbone and about 5-75% by weight of sidechains; wherein the acrylic polymer backbone contains pendent hydroxylgroups before the attachment of side chains by replacement of a hydrogenof at least one of the hydroxyl groups by the formula ##STR5## where Ris an aliphatic group, a cycloaliphatic group or an aromatic group; R¹is an alkylene group having 2-6 carbon atoms, R², which forms a sidechain, is a polymer segment of an acrylate polymer.
 2. The graftcopolymer of claim 1 having a weight average molecular weight of about5,000 to 1,000,000 determined by gel permeation chromatography.
 3. Thegraft copolymer of claim 2 in which the backbone is of polymerizedmonomers selected from the group consisting of alkyl methacrylate, alkylacrylate, hydroxy alkyl acrylate, hydroxy alkyl methacrylate andmixtures thereof.
 4. The graft copolymer of claim 3 in which R² is ofpolymerized monomers selected from the group consisting of alkylacrylate, hydroxy alkyl acrylates, hydroxy alkyl methacrylates andmixtures thereof.
 5. The graft copolymer of claim 2 in which thebackbone consists essentially of polymerized methyl methacrylate,2-hydroxy ethyl methacrylate and R² consist essentially of polymerizedbutyl acrylate and hydroxy ethyl acrylate and in which R iscyclohexylene and R¹ is --CH₂ --₂.
 6. The graft copolymer of claim 2 inwhich the backbone consists essentially of polymerized butyl acrylateand hydroxy ethyl acrylate and R² consist essentially of polymerizedmethyl methacrylate, butyl acrylate, hydroxy ethyl acrylate and acrylicacid and in which R is cyclohexylene and R¹ is --CH₂ --₂.
 7. A processfor preparing a graft copolymer of about 25-95% by weight of an acrylatepolymer backbone and about 5-75% by weight of side chains whichcomprises the following steps:(a) contacting a mercapto organicisocyanate of the formula ##STR6## with an acrylic polymer havingpendant hydroxy groups; wherein R is an aliphatic, cycloaliphatic oraromatic group;R¹ is an alkylene groups having 2-6 carbon atoms, and (b)adding acrylate monomers to the product resulting from step (a) andpolymerizing said monomers with the product of step (a) to form thegraft copolymer.
 8. The process of claim 7 in which step (a) is carriedout at about 80°-150° C. for about 0.5-6 hours in the presence of acatalyst and step (b) is carried out at about 60°-150° C. for about 1-6hours in the presence of a polymerization catalyst.